Segal's law
expressionops culturenetworking
A man with a watch knows what time it is; a man with two watches is never sure.
The proverb of conflicting authorities, and networking's favorite in-joke: it is literally why NTP exists and why serious timekeeping uses three or more sources with an algorithm to detect the liar. Two monitoring systems disagreeing about an outage is Segal's law with paging enabled.
A man with a watch knows what time it is; a man with two watches is never sure. Segal's law names the discomfort of contradictory measurements and the temptation to avoid them by measuring once.
The trap is that a single source of truth about the physical world is not accurate, it is merely unchallenged. One monitoring system reports availability and nobody argues, which feels like clarity and is actually the absence of a second opinion. When two systems disagree, at least one is wrong, and the disagreement is the only signal you will get that this was already true.
The engineering resolution is not to pick one watch but to understand why they differ. Two monitoring systems disagreeing about uptime usually differ in where they measure from, what counts as a failure, and how they average, and reconciling those definitions produces a better understanding than either number alone. The failure mode to avoid is deleting the second watch because it is inconvenient, which restores the comfort and removes the information.